The role of an automatic fire extinguishing installation implementing sprinklers is to detect, as early as possible, the seat of a fire then to automatically trigger the extinction system, at least locally, this while emitting an alarm. The installation has for objective to contain the fire as much as possible, before the arrival of the fire brigade which then takes over the installation in order to extinguish the fire.
In the field of the invention, firefighting installations are classified into three categories, namely:                “wet-pipe” systems;        “dry-pipe” systems;        “vacuum” systems.        
In these three systems, the sprinklers are mounted in a network in such a way as to be distributed evenly over the site to be protected. Conventionally, the sprinklers comprise:                a fixing connector, that allows the sprinkler to be connected to pipework, with this fixing connector having a nozzle intended for the passage of water to be released in order to extinguish the fire;        a fusible member;        a shutoff member for shutting off the nozzle, held in the shutoff position by the fusible member.        
The fusible member is calibrated to blow when a certain temperature has been exceeded, as such releasing the nozzle from its shutoff member.
In “wet-pipe” systems, the entire piping of the installation is filled with water, and this up to the sprinklers. The water is therefore on standby behind the shutoff means and when the fusible member blows, the water flows through the nozzle of the connector of the sprinkler of which the fusible member has blown.
The release time for the water is therefore immediate, which is particularly advantageous. On the other hand, “wet-pipe” systems, are not adapted for sites that have risks of freezing. Indeed, in case of freezing, the water cannot flow. In addition, the freezing can cause deteriorations to the piping of the installation (deformation and even bursting of the pipes). In certain cases, the installation is emptied of water. In other cases, the site to be protected is heated in order to prevent any risk of freezing. For sites to be protected that have a relatively substantial surface area, the consumption of energy, and consequently the heating bill, can be substantial, and even prohibitive. Another way to fight freezing is to add an antifreeze agent to the water of the installation, such as glycol which is a toxic and carcinogenic product.
In the “dry-pipe” systems, the entire installation is emptied of water. The entire piping of the installation is kept under pressure. When the fusible members blow, the air pressure is released by the sprinkler or sprinklers in question and the water, also under pressure, tends to “push” the air outside of the installation until it arrives at the orifice or orifices released in such a way as to escape through the latter.
With such a system, the water can in certain cases take up to 60 seconds to reach the sprinkler of which the fusible member is blown, which is of course compliant with the current standard but which can be excessively long with regards certain incipient fires.
In addition, “dry-pipe” systems do not entirely overcome the problems linked to freezing. Indeed, condensation can be created in the piping of a “dry-pipe” installation, which can damage certain components of the installation and cause the protection to fail.
Generally, “wet-pipe” and “dry-pipe” systems have the following disadvantages:                they are subject to forming slush and, consequently, to clogging;        they are subject to corrosion, which can obviously lead to an installation partially or entirely out of use and cause the protection to fail;        they can be the object of water leaks that cannot be seen;        they allow the development of microorganisms in the pipes of the installation.        
This results in that they require, among other things, antifreeze and anticorrosion treatments (involving recourse to harmful products).
Moreover, they require rinsing operations after use.
Furthermore, they imply putting into service times that are relatively long, according to the extent of the installation, which can range from one to four hours for “wet-pipe” systems and two hours and more for the “dry-pipe” systems.
In order to overcome all of these disadvantages, “vacuum” systems were designed. In “vacuum” systems, a vacuum is created in the pipes extending between a general valve and all of the sprinklers. In other terms, all of the pipes separating the valve from the sprinklers are in a vacuum.
In these systems, the vacuum constitutes an active energy which is used as a functional source in monitoring sprinklers. Indeed, if a fusible member of one of the sprinklers blows, the atmospheric pressure reaches the entire installation, which causes a change in the state of an actuator which, in turn, opens the general water inlet valve. Then the water quickly and without any obstacle invades the entire installation until the sprinklers, with the water flowing through the sprinkler or sprinklers of which the fusible member has blown. The vacuum which is still active in the networks quickly attracts the extinguishing water towards the sprinklers of which the fusible member has blown.
The triggering time of the actuator is very short, in that, when a fusible member blows, the “vacuum” installation immediately generates an aspiration phenomenon of the air outside of the installation. Note that this aspiration can be beneficial, as the aspiration effect on the seat of the fire tends to reduce the intensity of the latter.
The time for the water to arrive at the sprinkler of which the fusible member has blown is less than 60 seconds.
It is therefore understood that, due to the absence of water or of condensation in a “vacuum” system installation, the following results are obtained:                no corrosion, therefore no slush forming or clogging;        the guarantee of obtaining the density of extinguishing water required;        no development of microorganisms;        no water leaks possible (as the water is by default absent in the pipes of the installation that lead to the sprinklers);        no need for antifreeze agent or anticorrosion treatment;        no rinsing required before the installation is put into service.        
For certain installations, it is necessary to plan for the implementation of dry risers, used for fighting a fire that can break out in a cold room.
These dry risers provide the connection between a pipe of the network of “vacuum” sprinklers and the inside of the cold room. For this, the dry risers have an elongate body having at one of its ends a connecting piece for coupling to pipework and, at the other of its ends, a sprinkler of the type of that described hereinabove.
The height of the elongate body is sized according to the thickness of the thermally insulated wall of the ceiling of the cold room.
Of course, this size of the elongate body is such that the sprinkler borne by the lower end of the dry riser extends into the internal volume of the cold room.
The design of dry risers is provided in such a way that, when the network of sprinklers is filled with water, the dry risers for which the fusible members have not blown are not filled with water. Indeed, even after the network of sprinklers is placed in a vacuum, water could stagnate in the elongate body of a riser and, in light of the temperature in the cold room, would freeze. This would result in a failure of the riser in the situation of a fire inside the cold room for one and/or the other of the following reasons:                the atmospheric pressure cannot extend in the network of sprinklers due to the ice present in the elongate body impeding the penetration of ambient air of the cold room;        the water cannot flow through the sprinkler, also due to the ice present in the elongate body partially or entirely impeding the flow of water.        
In order to prevent this situation, dry risers include means of shutting off the connection, constituted by a first nozzle, between the riser and the pipework that bears it.
According to the operation of this dry riser, if the fusible member of the sprinkler of the riser blows, the shutoff valve on the sprinkler is ejected, which drives the displacement of the shutoff means on the first nozzle, in such a way as to release the communication between the riser and the pipework bearing the riser.
On the other hand, if the fusible member of the sprinkler of the riser does not blow, the shutoff means on the first nozzle remain in shutoff position and isolate the riser from the water present in the network of sprinklers.
However, according to the design of current risers and the corresponding maintenance practices, when the sprinkler of a dry riser has been triggered, the latter is entirely replaced.
As the cost of a single dry riser is relatively substantial, this maintenance practice is particularly expensive when it is a question of replacing all of the dry risers of a cold room.
Moreover, the sprinklers present at the mower end of the dry risers, as with all the other sprinklers of a “vacuum” network, comprise, in addition to the fusible member and the shutoff member, means for ejecting the shutoff member.
Indeed, as indicated hereinabove, when a fusible member blows, this results in an aspiration phenomenon of the air towards the inside the pipework of the installation. The shutoff member, if it is not forced to leave its location, remains somewhat “glued” on the mouth of the nozzle of the connector, which then does not allow the air to enter and consequently prevents the actuator from being triggered.
In order to prevent this, means for ejecting are mounted on each sprinkler. These means for ejecting are conventionally constituted of a spring inserted into a cylindrical part mounted in the nozzle of the sprinkler. An end of the spring is bearing against the bottom of the cylindrical part, while the other spring end is bearing against the shutoff valve held in position by the fusible member. The spring is of course in compressed state.
With such sprinklers, undesirable situations have sometimes been observed.
Indeed, it was observed that after blowing of the fusible member, the shutoff valve can remain in a partial shutoff position of the nozzle of the connector or in a position that hinders the proper distribution of the water. In any case, the spring is not ejected from the nozzle and therefore remains inside the latter.
This results in that, in any case, the nozzle is not entirely released, which forms a partial obstacle to the intake of air in the network. The consequence is that the vacuum of the installation is slowed down and, consequently, the triggering of the actuator is delayed, which can reach 30 to 40 seconds.